Gaseous electric discharge device



April 13, 1937. w. R. WALKER EAsEous ELECTRIC DISCHARGE DEVICE Filed July 16, 1954 INVENToR www //afew/ l Patented Apr. 13, 19,37

UNITED STATES PATENT OFFICE 2,076,756 GSEOUS ELECTRIC DISCHARGE DEVICE Application July 16, 1934, Serial No. 735,490

1 Claim.

The present invention relates to electric gaseous discharge devices generally and more particularly to apparatus for starting and operating the same.

5 A particular object of the invention is to improve the starting lof mercury vapor arc lamps and the like. A further object of the invention is to improve the operation of the vacuum switch which is employed in my novelcircuit. Other objects and advantages of my invention will appear from the following detailed description or from the accompanying drawing.

'I'he invention consists in a new and novel combination of elements as hereinafter set forth and l5 claimed.

In starting mercury vapor arcs of the Cooper Hewitt type it is customary to create a voltage surge of suilieient value to produce the necessary initial ionization by interrupting the flow of a current through the arc stabilizing inductance. Until recently this has been accomplished by the use of a highly evacuated mercury switch, called a shifter, but I have now found that greatly improved starting can be attained with a highly evacuated switch containing only solid contacts,

as is disclosed in my co-pending application, Serial No. 647,016, filed December 13,1932. In the use of the novel circuit there disclosed, however, it has been found that under some circumstances the switch again closes the circuit beforethe energy which is stored in the condenser of which.

the usual starting band is a part has been dissipated. Under these conditions the switch short circuits this condenser, and thus permits the flow of an extremely high current, far in excess. of

that for which the switch is designed. This excessive current flow tends to fuse the contacts of the switch, and thus is a source of considerable difficulty. I have nowdiscovered, however, that this difficulty can be entirely eliminated by a novel rearrangement of the elements employed in this circuit without in any way impairing the efciency thereof in initiating an arc.

According to my invention this new result is obtained by includinga resistance of the order of at least a few ohms in the circuit which includes both the shifter and the condenser of which the starting band is a part. In the preferred circuit this result is obtained by the novel expedient of 5 0 shifting the connection of the starting band from the usual point between the shifter and the current limiting resistance to a point beyond said resistance. As a result saiddresistance is given the new function of limiting the condenser discharge current flow through the shifter, as wellA as its former function of limiting the current flow therethrough from the line. With the cur-f rent which can flow through the switch or shifter as it closes thus limited the problem of insuring the opening of this switch is greatly simplified, 5 and at the same time the circuit is made exceedingly reliable and effective as a starting means for the mercury vapor arc, due to the fact that welding of the switch contacts is positively precluded. l0

For the purpose of illustrating my invention I have shown a schematic diagram of a preferred embodiment thereof in the accompanying drawing.

Asl shown in this drawing the mercury vapor l5 arc lamp I of the well known Cooper Hewitt type has a mercury cathode 2, a conventional starting band 3 of tinfoil or the like in electrostatic relation thereto, and a pair of anodes 4. The anodes 4 are each connected in the usual manner through 20 a ballast resistance 5 to an end of the autotransformer 6, said autotransformer being connected in turn to any suitable source of alternating current. The cathode 2 is likewise connected in the usual manner through an arc stabilizing in- 25 ductance 1 to the midpoint of said autotransformer 6. A highly evacuated, solid contact switch 8, which is preferably of the type disclosed in my Patent 1,984,505, granted December 18, 1934, is arranged to be magnetically opened 30 by said inductance. One terminal of said switch, or shifter, as it is commonly calledis connected to the same side of the inductance as is the cathode 2, while the other terminal of said switch is connected through a resistance 9 of the order of 35 at least a few ohms,` and preferably of from to ohms, to one end of said autotransformerV 6 through one of said ballast resistances 5. The

starting band 3 is connected to a point between said resistance 9 and the resistance 5.. 40

In the use and operation of this device, upon application of a suitable alternating current potential to the autotransformer 6 potential is applied between the anodes 4 and the cathode 2, but this potential is insufficient to initiate a dis- 45 charge therebetween, as is well known. A current of the order of an ampere flows, however, from the midpoint of the autotransformer 6 through the inductance 1, shifter 8, the current limiting resistance 9 and` ballast resistance 5 50 back to one end of said autotransformer. This current energizes said inductance and thus opens the shifter 8. A voltage surge is thereupon created within said inductance 1 which depresses the potential of the cathode 2 a thousand volts 55 of an arc discharge from the anodes 4 to the cathode 2 at the existing potential ydifference therebetween. course, discharged when this disruptive discharge occurs. In some cases, however, the surge may fail of its purpose, so that this condenser is still charged when the shifter 8 again closes, forming a closed circuit from the mercury cathode 2 through the shifter 8, and resistance 9 back to the starting band 3. vThe condenser is thereby l discharged, but the current is limited by the resistance 9 to a value which the shifter 8 can control without diillculty, whereas in the absence of the resistance 9 in this circuit this current reaches such proportions that the contacts of the shifter frequently weld together, rendering the entire .lamp inoperative. Hence as a result of this novel location of the resistance 9 with respect to the vacuum shifter 8 and the starting band 3 I have been able to eliminate a serious diftlcultywhich threatened to limit the use of a shifter of thistype in a lamp startingl circuit. I have furthermore found that the presence vof this low resistance in this location in the starting circuit does not result in any appreciable impairment of the starting of the lamp I, but .that on the contrary it tends to improve it due to the better operation of the shifter 8.

While I have described my invention by ref .erence to a specific embodiment thereof it is to` 4Q be understood that it is not limited thereto, but

The aforesaid condenser'is, of

that it is likewise applicable to use in starting problem is encountered, and that various omissions, substitutions and changes, within the scope voi the appended claims, may be-made therein without departing from the spirit thereof.

I claim as my invention:'v I In combination, a mercury vapor arc device 'having a mercury pool cathode, at least one anode, and a conducting sheath for starting said arc .in electrostatic relation toA said pool, wheref by said pool and said sheath form the plates of a condenser, a connection from said sheath to la point o f substantially constant potential during the starting operation of the lamp, an inductance in the lead to saidcathode, means to complete va circuit through said inductance independently of said device, said means including an evacuatedv metal to metal contact switch which also `completes a .circuitthrough said condenser and which is magnetically responsive to current flow through said inductance to open said circuit therethrough whereby a voltage surge is created' which increases the potential difference between said cathode and said sheath and thus charges said condenser, an impedance path around-said switch through which the charge on said condenser can escape, said switch having an inertia such thatvit opens and again closes*y the circuits therethrough before the condenser is completely discharged through said impedance path, and a resistance included within the aforesaid circuit containing said switch and condenser which limits' the condenser dischargel current through said switch to a value which will not' fuse said contacts when said contacts reclose before the condenser charge has been dissipated.

uWARREN R. WALKER.

' any type of discharge device wherein asimilar. 'n 

